1. Field of the Invention
The present invention relates to a technology for reducing a natural disaster relating to a landslip, and more particularly, to a ring shear apparatus that may measure a shear strength that is a significant factor in evaluating the mobility of the landslip.
2. Description of the Related Art
Landslips take place when a soil mass slides along a thin soil layer above a bedrock due to external causes, such as an earthquake, isolated t-storms, thawing, and the like. Landslips in Korea usually take place due to isolated t-storms.
Slopes formed by landslips form action destructive surfaces gradually and undergo continuous sliding (slope action) and debris flow. For these reasons, the movement of a landslip is interpreted by dividing the landslip into (1) before destruction, (2) destruction, and (3) movement after destruction.
The soil mass in an area where a landslip takes place along the action destructive surfaces undergoes saturation and unsaturation repeatedly due to a change of rainfall and shows continuous strain. The stability of natural slopes is determined by strength characteristics (drainage and non-drainage shear strengths) as functions of time and strain. Shear strengths caused by strain before destruction are related to an early warning system for slopes and are essential parameters in evaluating the stability of slopes. The occurrence of the debris flow that corresponds to movement after destruction is directly related to a damage of infrastructure.
‘A landslip that moves very slowly’ corresponding to a stage before destruction proceeds at a speed of less than 10−6 cm/s. In this case, the soil mass on the natural slopes shows a progressive action, and it is difficult to identify movements of the slopes with naked eyes. The movement speed of the soil mass after the slopes reach destruction, is usually within a range of 0.1 cm/s. The movement of a landslip that moves faster than the movement speed of the soil mass within 0.1 cm/s is referred to as ‘a landslip that moves very quickly’, and the proceeding speed of the landslip that moves very quickly is generally 5 cm/s. In addition, when the soil loses its own soil strength, like liquefaction of sandy soil, due to the landslip, the debris flow occurs, and deposits move like a fluid, and the maximum movement speed of the deposits is 10 m/s.
Large and small landslips in Korea that take place due to annual isolated t-storms make living rights to be deteriorated, accompanied by social and economical losses over the living of people. In this way, the development of a test apparatus for predicting an unexpected landslip and evaluating the mobility of the debris flow that will occur after destruction is required. In particular, the development of a test apparatus that may perform quantitative measurement of a shear strength of the soil by varying a significant condition in a landslip, i.e., a saturation or unsaturation condition, a drainage or non-drainage condition, and a compaction or non-compaction condition, is needed.
Soil samples are accommodated in an upper ring and a lower ring of a general ring shear apparatus. A wall-slip effect that, when the upper ring and the lower ring are rotated relative to each other, the soil samples are slid on inner circumferential surfaces of the upper ring and the lower ring, occurs. If the soil samples are slid between the upper ring and the lower ring, a torque of the ring shear apparatus is decreased, and an error occurs when the shear strength of the soil is measured at the upper ring and the lower ring.
Thus, ring shear apparatuses that may measure a shear strength of the soil precisely by preventing soil samples from being slid on wall surfaces of an upper ring or a lower ring have to be developed.